This invention relates to motor control systems, and in particular, to an interface module which allows a user to set the operating parameters of an AC induction motor from a remote location.
There are two basic approaches for controlling the starting, stopping and speed of an AC induction motor. In a first approach, an adjustable frequency controller is interconnected to the AC induction motor. The adjustable frequency controller is comprised of an inverter which uses solid state switches to convert DC power to stepped waveform AC power. A waveform generator produces switching signals for the inverter under control of a microprocessor. While adjustable frequency controllers efficiently control the motor speed and the energy used by an AC induction motor, use of such types of controllers may be cost prohibitive. Further, since many applications of AC induction motors do not require sophisticated frequency and voltage control, an alternative to adjustable frequency controllers has been developed.
An alternate approach to the adjustable frequency controller is the soft starter. Soft starters operate using the principal of phase control whereby the three phase main supply to the AC induction motor is controlled by means of anti-parallel thyristor switches in each supply line. In phase control, the thyristor switches in each supply line are fired to control the fraction of the half cycle over which current is conducted to the motor (known as the conduction period). The non-conducting period of each half cycle (known as the hold-off angle or the notch width) is visible as a notch in the voltage waveform at each motor terminal. During this period, no current flows to the motor terminals. To end the non-conducting period, the thyristor switches in the supply line to the motor terminals are fired to restart their conduction. The conduction through the thyristor switches continues until the current, once again, becomes zero at some point in the next half cycle and the thyristor switches reopen. According to the principles of phase control, by varying the duration of the non-conducting period, the voltage and current supplied to the AC induction motor may be controlled. As is known, a single microprocessor has been used to fire the thyristor switches in order to control the voltage and current supplied to the AC induction motor.
In order to accurately control the starting, stopping and speed of the AC induction motor, the microprocessors used in adjustable frequency controllers and the soft starters must execute extensive control algorithms. High performance microprocessors are necessary to perform the numerous calculations required at an acceptable computational speed. The types of high performance microprocessors are expensive and increase the overall cost of the motor control. Therefore, it is highly desirable to provide a motor control system which provides the desired control of the motor at a lower cost.
In addition, use of a single microprocessor in motor control applications limits the flexibility of such motor control. Heretofore, motor controls have been built as single, integral units. Such units provide for limited input and output options for the user. As a result, prior art motor controls limit a user's ability to monitor certain operating parameters or require special hardware to order to have certain operating parameters displayed or controlled. Therefore, it is highly desirable to provide a motor control which allows for greater flexibility for the users thereof.
Therefore, it is a primary object and feature of the present invention to provide a motor control system which incorporates distributed processing to reduce the cost and improve performance of the motor control system.
It is a still further object and feature of the present invention to provide a motor control system which increases the flexibility for the users thereof
It is a still further object and feature of the present invention to provide an input/output device for a motor control system which is simple to use and inexpensive to manufacture.
In accordance with the present invention, an interface module is provided for allowing a user to set the operating parameters for the starting, stopping and control of a motor with a motor control. The motor control being operatively connected to a communications network. The interface module includes a micro-controller for providing instruction signals to the motor control in order to set the operating parameters of the motor. A plurality of input devices are operably connected to the micro-controller. Each input device provides a control signal to the micro-controller, which, in turn, generates an instruction signals in response thereto. A communications link interconnects the micro-controller to the communications network. The communications link transmits the instruction signals from the micro-controller to the motor control over the communications network.
It is contemplated to operatively connect a visual display structure to the micro-controller in order to provide a visual display for the user. It is contemplated that the communications link receive a packet of data from the motor control over the communications network and provide the same to the micro-controller such that the visual display structure is activated by the micro-controller in response to receipt of a predetermined packet of data by the micro-controller.
The plurality of input devices may include a trip selection device operatively connected to the micro-controller and movable between a first enabled position wherein the micro-controller trips the motor in response to a predetermined condition thereon and a second disabled position wherein the micro-controller continues operation of the motor in response to the predetermined condition thereon. A reset selection may also be operatively connected to the micro-controller. The reset selection is movable between a first manual reset position wherein the motor must be manually restarted if the motor is tripped and a second auto reset position wherein the micro-controller automatically restarts the motor after a predetermined period of time if the motor is tripped.
A plurality of input devices may also include a first start selection device operatively connected to the micro-controller. The first start selection device is movable between a first start position when the motor control provides constant energy to the motor during starting of the motor and a second start position wherein the energy supplied to the motor during the starting of the motor is increased over time. First and second trip class selection devices may also be provided. Each trip class selection device is movable between first and second positions such as each combination of trip class selection device positions corresponds to a predetermined time period that an overload condition on the motor can exist before the motor control trips the motor.
The interface module of the present invention may also include a first kick start potentiometer having a user selected resistance thereacross. The user selected resistance thereacross determines a time period that the motor control increases the voltage to the motor during start-up to overcome the inertia of the motor. A second kick start potentiometer may also be provided for varying the magnitude of the voltage provided to the motor by the motor control during such time period.
A first ramp potentiometer also has a user selected resistance thereacross. The user selected resistance across the ramp potentiometer determines a time period that the motor control ramps the motor to its operating speed. A second ramp potentiometer also has a user selected resistance thereacross. The user selected resistance across the second ramp potentiometer determines an initial energy level being delivered to the motor when the motor control begins ramping the motor to its full operating speed. A deceleration potentiometer also may be provided. The deceleration potentiometer has a user selected resistance thereacross which varies the deceleration time of the motor from its full operating speed to full stop.
In accordance with a further aspect of the present invention, an interface module is provided for allowing a user to set the operating parameters of the motor driven by a motor control. The motor control is operatively connected to a network. An interface module comprises a micro-controller for generating instruction signals to the motor control. A communications link interconnects the micro-controller to the H network for receiving packets of data from the motor control over the network and providing the same to the micro controller. In addition, the communications link transmits the instruction signals from the micro-controller to the motor control over the network. A visual display structure is operatively connected to the micro-controller for providing a visual display to the user in response to a predetermined packet of data received by the micro-controller from the communications link. A user interface structure allows the user to set the operating parameters for the motor. The user interface structure provides corresponding parameter signals to the micro-controller such that micro-controller generates the instruction signals in response thereto.
It is contemplated that the user interface structure include a selection device having a plurality of user selected positions. Each position of the user selection device sets one of the operating parameters of the motor. The user interface module may also include a potentiometer having a user determined voltage thereacross. The voltage across the potentiometer being a predetermined parameter signal corresponding to the setting of one of the operating parameters of the motor.
It is contemplated that the micro-controller include a universal asynchronous receiver/transmitter which is operatively connected to the network. It is further contemplated that the visual display structure includes a plurality of LEDs. Each LED corresponds to a predetermined air condition on the motor.
The micro-controller may also include an analog-to-digital converter for converting the parameter signals received to corresponding digital parameter signals. The micro-controller also includes a plurality of micro-controller executable instructions stored thereon. The micro-controller executable instructions include the steps of monitoring the network with the communications link and activating the visual display in response to a predetermined packet of data. The micro-controller reads the parameter signal for the user interface structure and generates instruction signals responding to the parameter signals read from the user interface structure.
In accordance with a still further aspect of the present invention, a method for setting a parameter of a motor driven by a motor control is provided. The motor control is interconnected to a communications network. The method includes the steps of interconnecting an interface module to the communications network. The interface module includes an input device which allows the user to set a desired parameter for the motor. An instruction signal is generated in response to the user selected setting and transmitted to the motor control over the communications network. The method may also include any additional step of determining the type of motor control interconnected to the communications network by broadcasting an initialization signal on the communications network with the interface module and receiving a response from the motor control. The step of setting the input device may include the step of switching a selection device to a desired position corresponding to the desired setting for the parameter or the step of setting a potentiometer to a predetermined resistance corresponding to a desired setting of the parameter of the motor.
The method may also include the additional steps of monitoring the communications network for error signals from motor control and generating a visual display in response thereto.